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Empirical Validation of a Transient Computer Model for Combined Heat and Moisture Transfer.

pdf icon Empirical Validation of a Transient Computer Model for Combined Heat and Moisture Transfer. (1361 K)
Rode, C.; Burch, D. M.

U.S. Department of Energy (DOE); Oak Ridge Natiional Laboratory (ORNL); American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE); Building Environment and Thermal Envelope Council (BETEC). Thermal Performance of the Exterior Envelopes of Buildings VI Conference. Proceedings. Thermal VI. December 4-8, 1995, Clearwater Beach, FL, 283-295 pp, 1995.


heat transfer; moisture; validation; computer models; condensation; mass transfer; measurement; modeling; siding


A computer program for transient modeling of combined heat and moisture transfer in building constructions is introduced. The model's predictions are compared against moisture content and heat flux data obtained for six typical North American lightweight wall constructions that have been exposed to climatic conditions in a calibrated hot box. A special aspect of the work was that the basic moisture and thermal transport properties were determined for each individual material in the walls. The experiment, and thus the validation, was restricted to diffusive transport mechanisms taking place in the hygroscopic region. Using the detailed information on the material properties, the program was able to predict the measured moisture content of the walls' siding and sheathing materials to within approximately 1% moisture content by weight, and the heat flows were predicted with a satisfactory accuracy. In a subsequent sensitivity andalysis, the moisture transport properties were described as simpler functions or selected arbitrarily from a database of ordinary building materials. In some cases, this had a noticeable effect on the resulting moisture contents. It is suggested that transient heat and moisture transport models can be used in the design and analysis of constructions if the user is knowledgeable about the workings of such models and cautious in interpreting the results.